1. Field of the Invention
The present invention relates to a method and apparatus for the automated analysis of chemical plant process streams and in particular to a method and apparatus for the automated analysis of a liquified hydrocarbon stream such as isobutane feed to a propylene oxide/tertiary butyl alcohol plant to monitor the inorganic chloride content of the hydrocarbon feed.
2. Description of the Prior Art
In many industrial chemical plant processes, problems arise as a result of the presence of chloride or chlorine containing compounds in hydrocarbon feed streams. For example, isobutane is an essential feed stream to commercial plants which co-produce propylene oxide (PO) and tertiary butyl alcohol (TBA) by procedures described, for example, in U.S. Pat. No. 3,351,635. Experience has shown that the inorganic chloride content of the feed isobutane can fluctuate rapidly and widely in commercial practice. The introduction of chlorides such as iron chloride to a PO/TBA plant can cause serious problems including chloride stress cracking of stainless steel components, leakage and plant shutdown.
Current techniques for monitoring the chloride content of hydrocarbon feed streams such as isobutane involve manually obtaining feed samples under conditions of elevated pressure, transport of the samples to a testing laboratory where the samples are manually extracted by an aqueous wash and then titrated with silver nitrate for chloride content. Although such techniques are quite accurate, they are labor intensive and are unable to produce results quick enough so that prompt measures can be taken to prevent contamination of the plant.
U.S. Pat. No. 4,942,133 provides a procedure for the continuous analysis of the chloride ion content of overhead waters downstream of a hydrocarbon distillation column, but this does not relate to automated chloride analysis of hydrocarbon feed to a chemical plant.
U.S. Pat. No. 4,650,768 relates to automated methods for determination of chloride in an aqueous fluid sample, but this does not relate to automated chloride analysis of hydrocarbon feed to a chemical plant.